Dissolve cornstarch in chicken broth in a bowl. Stir in soy sauce, ginger, and hot sauce; set aside.
Heat 1 tablespoon oil in a wok or large skillet over high heat. Add chicken; cook and stir until no longer pink, about 5 minutes. Transfer chicken to a plate; set aside.
Add remaining 1 tablespoon oil to the wok. Add onion, green bell pepper, and water chestnuts; cook and stir until chestnuts are hot and onion has softened, about 5 minutes. Stir reserved sauce to redistribute cornstarch; add to the wok and bring to a boil. Add reserved chicken; stir until sauce thickens, and chicken is hot. Sprinkle with cashews to serve.
